It has long been known that increasing the compression ratio of an internal combustion engine increases its thermodynamic efficiency. It has also been long known that if the geometric volume ratio remains constant (i.e., a fixed volume combustion chamber), the pressure ratio is decreased, resulting in a mixture in the combustion chamber whose pressure is below that obtained at full throttle. One approach to restoring the full pre-combustion pressure (or achieving the desired pressure ratio) is to vary the volume of the combustion chamber.
Similarly, it has been long understood that sleeve valves are more efficient and less complex than traditional “poppet” valves.
Designs for variable volume combustion chambers are numerous. Likewise there are several designs for sleeve valves. The present invention integrates both concepts into one design to realize the cumulative benefits.
Sleeve Valve:
In 1908 Charles Knight invented the sleeve valve for use in internal combustion engines. The design had two cast-iron sleeves per cylinder, one sliding inside the other, with the piston inside the inner sleeve. The sleeves were operated by small connected rods actuated by an eccentric shaft and had ports cut out at their upper ends. The cylinder head was like a fixed piston, with its own set of rings projecting down inside the inner sleeve. The heads were individually detachable for each cylinder. The design allowed a more central location for the spark plugs, large ports for better gas flow, and hemispherical combustion chambers that in turn gave increased power. In addition, the sleeve valves required much less maintenance than poppet valves, which needed adjustment, grinding, and even replacement after a few thousand miles.
The sleeve valve concept was also envisaged by Peter Burt (Letter Patent No GB 190,918,140) and James McCollum (Patent No GB 190,914,629).
There have been several variations of the Knight invention over the years. U.S. Pat. No. 4,487,172A is a typical example. It is a single-sleeve valve engine with narrow quasi-elliptic sleeve motion that improves exhaust and intake valving and permits the conversion of standard engine blocks. The sleeve is thick walled, and is molded of low density material which permits significant rounding of the sleeve apertures for better flow, and grooves and rings for oil control, gas leakage reduction, and mass reduction. The sleeve has an extension which projects above the head and is connected to a half-speed crankshaft by means of a connecting rod. This connecting rod is restrained at an intermediate point by a radius rod to obtain quasi-elliptic sleeve motion which has an amplitude approximately half as great circumferentially as axially. In order to minimize emissions, provision is made for swirl, scavenging, multiple spark plugs, and a near ideal combustion chamber shape.
Variable Volume Combustion Chamber:
U.S. Pat. No. 741,824 by Pehrsson describes a 4-stroke, internal combustion engine with a cam operated exhaust valve and a vacuum operated intake valve, and with a main cylinder-diameter auxiliary piston used to manually vary the combustion chamber volume, to obtain the maximum pre-combustion pressure. The position of the auxiliary piston defines the limits of travel of the inlet valve.
In U.S. Pat. No. 1,167,023 by Schmidt, there is disclosed a conventional 4-stroke engine with an auxiliary cylinder and piston above the main cylinder, to vary the combustion chamber volume. The auxiliary piston position is controlled by a spring, and the load of combustion is taken up by hydraulic pressure. The position of the auxiliary piston is therefore dependent on the load, as the rate of supply and escape of oil from above the auxiliary piston (or the top half of it) is limited by the rate with which it can enter or escape through the oil ports. The outlet port has a valve that has a preset (and alterable) pressure relief system. If the combustion pressure exceeds this pressure, oil is forced out of the pressure chamber, and the auxiliary piston moves towards its outermost position, increasing the combustion chamber volume. When the load setting is decreased, and the combustion pressure is less than this value, oil is not released from the outlet, but still enters through the inlet check valve, resulting in the movement of the piston towards the main cylinder, and increasing the pre-combustion pressure.
Wilson discloses in U.S. Pat. No. 1,639,477 a conventional 4-stroke engine with an auxiliary cylinder and multiple crowned piston located above the working piston. The position of the auxiliary piston is controlled by the pressure in the intake manifold, via a second auxiliary piston, operated upon by hydraulic pressure. A spring is used to move the auxiliary piston to its outermost position when the engine is not running.
In U.S. Pat. No. 2,142,466 by Wagner a conventional 4-stroke compression ignition engine is described, with a throttled intake system and a variable volume combustion chamber. The auxiliary piston reciprocates, driven by the camshaft, whose timing is variable angularly.
In U.S. Pat. No. 2,344,993 by Lysholm there is disclosed a conventional 4-stroke spark or compression ignition engine with closure of the intake valve during the intake stroke, executing the Atkinson cycle. As the piston speed is high during valve closure, at high engine speeds the volumetric efficiency of the engine is reduced. If the intake valve were to be closed on the compression stroke instead, then the volumetric efficiency at high engine speeds would be increased, necessitating reducing it at low speeds. By closing the intake valve later on the induction stroke, and opening it very briefly on the compression stroke, the patent claims to produce a nearly constant volumetric efficiency, or that almost any desired curve of volumetric efficiency with engine speed can be tailored. On the compression ignition engine, the valve opening on the compression stroke can be the exhaust valve, as the fuel has not been injected as yet. The patent indicates that this is most suited to supercharged engines, thus in effect raising the efficiency to levels at or slightly above non-forced induction engines.
In U.S. Pat. No. 2,467,568 by Rosaen there is disclosed a conventional 4-stroke engine with a variable volume combustion chamber, controlled by hydraulic pressure. It appears that the auxiliary piston is filled with oil.
Humphreys discloses in U.S. Pat. No. 2,769,433 a conventional 2-stroke or 4-stroke engine with an auxiliary cylinder and piston located above the working piston. The auxiliary piston is backed by hydraulic fluid supplied by the engine's lubrication system. Oil can escape from the chamber at the back of the auxiliary piston if the maximum pressure achieved during combustion exceeds a preset value, which is enforced on the escape mechanism.
Heisling discloses in U.S. Pat. No. 2,883,974 a conventional 4-stroke engine with an auxiliary cylinder and piston located above the working piston, whose purpose is to provide a variable volume combustion chamber. The position of the auxiliary piston is controlled by hydraulic pressure, and it is also actuated by hydraulic pressure. A second embodiment utilizes a moving cylinder sleeve. Much of the emphasis of the invention is on the control mechanism to make the idea work.
In U.S. Pat. No. 3,964,452 by Nakamura an auxiliary cylinder and piston are located above a main cylinder and piston, and may communicate with them. A spring loaded piston may slide in the auxiliary cylinder, and does so after a certain preset high pressure is achieved during combustion. The primary purpose is to limit pressures and temperatures during combustion, and therefore increase thermal efficiency while ensuring that production of NO is limited. Lean charges lead to reduced CO and HC emissions, but they may also produce misfires and combustion fluctuations.
In U.S. Pat. No. 4,033,304 by Luria there is described an internal combustion engine that achieves constant pre-combustion pressure with a movable auxiliary piston and cylinder, wherein said piston is controlled by hydraulic means. The invention implements the Atkinson cycle with variable inlet valve timing. The inlet valve is held open past bottom dead center (“BDC”) to vent the unwanted mixture back into the inlet tract. The auxiliary piston is spring loaded so that during the exhaust stroke, the auxiliary cylinder volume is at its least, thereby scavenging.
In U.S. Pat. No. 4,187,808 by Audoux there is disclosed a conventional 4-stroke engine, with an auxiliary piston and cylinder located above the main piston. The focus is on the hydraulic valving used to reduce any loads on the mechanical actuation of the auxiliary piston. With lowered pressure in the main cylinder, the auxiliary piston is designed to move inward towards the main cylinder, decreasing the volume of the combustion chamber, and assisting in scavenging burnt gases.
U.S. Pat. No. 4,516,537 by Nakahara discloses a conventional 4-stroke engine with an auxiliary cylinder and piston located in the head above the main piston and cylinder. The auxiliary piston is moved by hydraulic fluid under pressure. A major thrust of the invention is to construct a feasible means of controlling the auxiliary piston position, without having the excessive pressures from combustion having an impact on the oil pressure system, yet to distribute the load uniformly.
U.S. Pat. No. 4,798,184 by Palko discloses a 2-stroke or 4-stroke diesel engine where the intake valve is closed on the compression stroke to implement a greater expansion duration than compression. The valve actuation means is not described in any detail, and the patent indicates that it may be fixed or it may be variable during operation. The extended expansion allows combustion to occur at or after top dead center (“TDC”), reducing engine loads, and heat losses to the cooling system. The usual advantages to the expansion increase are more work produced by the expanding gases, and lower exhaust temperatures.
U.S. Pat. No. 5,003,936 discloses a variable volume cylinder where the cylinder head of the cylinder has arranged therein an insert whose position is hydraulically adjustable, the compression chamber being enlarged by lifting the insert, while it is reduced by lowering the insert. The position of the insert is controlled through a microprocessor in conjunction with a lambda probe.
U.S. Pat. No. 5,054,438 discloses a floating cylinder for a two cycle internal combustion engine providing a cylinder movably held within the cylinder block. The ports operation timing is controlled by a longitudinal movement of the cylinder.
U.S. Pat. No. 5,341,771 by Riley discloses a 2-stroke or 4-stroke engine where a hydraulically controlled auxiliary piston can be withdrawn to vary combustion chamber volume in response to engine load (idle to full). Traditional valves are used for intake and exhaust.
The present invention features a variable volume combustion chamber with an integral sleeve valve system for four-cycle combustion engines. The variable volume chamber is controlled via a microprocessor-controlled solenoid.
Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this specification, and the knowledge of one of ordinary skill in the art. Additional advantages and aspects of the present invention are apparent in the following detailed description and claims.